1. Field of the Invention
The present invention relates to a coffee brewing apparatus, which is used particularly in an automatic coffee dispenser.
2. Description of the Prior Art
One of popular coffee brewing methods is to pour hot water onto ground coffee so that the hot water extracts coffee ingredient while passing through the ground coffee. In a simple method, the hot water passes down through the ground coffee by its own gravity. There is also a conventional method in which the hot water is forced to pass through ground coffee under pressure.
FIG. 3 shows a conventional coffee brewing system used in an automatic coffee dispenser. The system includes a water supply line 210, a water shutoff valve 211, a water heater 212, a hot water supply line 213, a hot water shutoff valve 214, and a coffee brewing apparatus 200, which is shown in elavational section.
The coffee brewing apparatus 200 includes a hot water supply cylinder 201 for containing hot water, a piston 202, a cylindrical ground coffee holder 203, a strainer 204 and a coffee outlet funnel 205. The top open end of the ground coffee holder 203 is removably and sealingly fitted to the bottom open end of the hot water supply cylinder 201. The strainer 204 is tightly interposed between the ground coffee holder 203 and the coffee outlet funnel 205. The piston 202 is adapted to sealingly and slidingly fit the hot water supply cylinder 201 internally.
A predetermined quantity of ground coffee 203c is deposited in the holder 203 before it is fitted to the hot water supply cylinder 201. The water provided through the water supply line 210 to the water heater 212 is heated up to a near boiling temperature at a regulated pressure. A predetermined quantity of hot water 201w is provided from the water heater 212 into the hot water supply cylinder 201 through the hot water supply line 213 by opening the valve 214 for a predetermined time period. Then, the piston 202 is lowered into the cylinder 201 so that the hot water 201w in the cylinder 201 and most of the air trapped in the cylinder 201 are forced down through the ground coffee 203c in the holder 203. The hot water extracts coffee ingredient from the ground coffee 203c while passing therethrough and comes out through the strainer 204 and the coffee outlet funnel 205, as shown by an arrow in FIG. 3.
Another popular conventional coffee brewing method is to deposit ground coffee into hot water and blow air into the mixture of the hot water and the ground coffee so that the ground coffee is agitated in the hot water. This method, however, is not adequate for producing strong coffee because it requires a comparatively large quantity of hot water per unit quantity of ground coffee.
Whereas some disadvantages are known pertaining to the method by the apparatus 200 shown in FIG. 3. Since the ground coffee 203c is loosely deposited in the ground coffee holder 203, granules of the ground coffee 203c tend to shift from one place to another in the holder as the hot water flows down in the holder. This results in a creation of a partial hot water flow path in the holder, which is known as "channeling". The channeling effect causes the ground coffee in the holder to be subjected to the hot water unevenly. Since the channeling occurs randomly in the holder, coffee liquid of varied density tends to be produced in each coffee making process. In the above described coffee brewing method by the apparatus 200, the hot water starts to flow down through the ground coffee as soon as the cylinder 201 starts receiving hot water before the piston 202 enters the cylinder 201 to force the hot water down. This early flow of hot water also causes undesirable "channeling" in the ground coffee.